Outline

Objective

The authors of the Ocular Hypertension Treatment Study (OHTS) have concluded that a clinician caring for a patient with ocular hypertension can assess that individual's risk of developing primary open angle glaucoma by considering central corneal thickness among other factors. Further randomized clinical studies concerning the importance of corneal thickness in the diagnosis of glaucoma are not available. Because the validity of a statement is strongly associated with randomized studies in evidence based medicine corneal thickness could only be considered as a risk factor in an evidence based glaucoma diagnostic process. There are, however, associations in medicine whose existence can not and should not judged by the way of thinking which has been initiated by Sackett. In using the term "evidence based medicine" it has to be regarded that in the literature it has been used almost exclusively as "evidence based therapy". Evidence in biophysics and biochemistry has still to be judged by the accepted rules in physics, chemistry and biometry (biostatistics).

Methods

The literature has been analyzed on which the authors of the OHTS based their working hypothesis corneal thickness being a risk factor. It shows that the authors don't differentiate between two clearly different associations: the association between corneal thickness and a difference of pressure values (intracameral and by applanation) and the association between corneal thickness and sole applanation values. The authors of the OHTS additionally base their hypothesis on results which are biometrically not convincing.

Results

The special working hypothesis shows a lack of evidence according to the rules of thinking in physics and biometry.

Conclusions

There is undoubtedly an association between corneal thickness and glaucoma damage of the optic nerve head but it is not evident postulating central corneal thickness being a risk factor. It is evident from a biophysical point of view that this association is due to the influence of corneal thickness on the results of applanation tonometry.